protoplanet

noun

pro·​to·​plan·​et ˈprō-tō-ˌpla-nət How to pronounce protoplanet (audio)
: a hypothetical whirling gaseous mass within a giant cloud of gas and dust that rotates around a sun and is believed to give rise to a planet
protoplanetary
ˌprō-tō-ˈpla-nə-ˌter-ē How to pronounce protoplanet (audio)
adjective

Examples of protoplanet in a Sentence

Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Beyond the question of how an angrite-spawning protoplanet could have arisen so early on, the details of its demise are unknown. — Jenna Ahart, Scientific American, 9 June 2026 As collisions with the dust and gas reduced them, more would spiral in from the outer solar system to keep feeding the decay until the protoplanets made their final fatal plunge. — New Atlas, 11 Nov. 2025 The cloud's relatively close proximity to Earth lends it to further study by astronomers wanting to learn more about how stars, and the protoplanets that circle them, form. — Jeffrey Kluger, Time, 18 Dec. 2025 It's thought to be the result of collisions with various protoplanets and other massive objects during the formation of the solar system billions of years ago, according to NASA. — Janet Loehrke, USA Today, 17 June 2026 See All Example Sentences for protoplanet

Word History

First Known Use

1949, in the meaning defined above

Time Traveler
The first known use of protoplanet was in 1949

Rhymes for protoplanet

See All Rhymes for protoplanet

Browse Nearby Words

protophyte
protoplanet
protoplasm
See all Nearby Words

Cite this Entry

“Protoplanet.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/protoplanet. Accessed 7 Jul. 2026.

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Kids Definition

protoplanet

noun
pro·​to·​plan·​et ˈprōt-ō-ˌplan-ət How to pronounce protoplanet (audio)
: a whirling mass of gas that rotates around a star and is believed to become a planet
protoplanetary
ˌprōt-ō-ˈplan-ə-ˌter-ē How to pronounce protoplanet (audio)
adjective

More from Merriam-Webster on protoplanet

Britannica.com: Encyclopedia article about protoplanet

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